1. Field of the Invention
The present invention relates to a mat, a method for manufacturing the mat, and an apparatus for purifying exhaust gas.
2. Discussion of the Background
Conventionally, a non-woven mat formed by laminating inorganic fibers such as silica and alumina fibers has been known, and has been used for various applications since the mat is superior in characteristics such as heat resistance and elasticity (repulsive force).
For example, the mat is used as a member forming the apparatus for purifying exhaust gas.
As specifically described, the general apparatus for purifying exhaust gas includes an exhaust gas treating body, a casing housing the exhaust gas treating body, and a holding sealing material placed between the exhaust gas treating body and the casing. The above-mentioned mat is used as a member forming the holding sealing material. The holding sealing material is manufactured through a process of cutting the mat into a predetermined shape, and the like.
A holding sealing material made of a non-woven mat having a repulsive force has a predetermined holding force. For this reason, in the apparatus for purifying exhaust gas, the holding sealing material tightly holds the exhaust gas treating body at a predetermined position in the casing. Since the holding sealing material is placed between the exhaust gas treating body and the casing, if vibration or the like, is caused, the exhaust gas treating body is less likely to come into contact with the casing, and exhaust gases are less likely to leak from between the exhaust gas treating body and the casing.
Herein, examples of a method for manufacturing the apparatus for purifying exhaust gas using the holding sealing material include, for example, a method for stuffing the exhaust gas treating body wrapped with the holding sealing material into the casing.
To make it easy to stuff the exhaust gas treating body into the casing in the manufacturing method, it is necessary to moderately reduce the bulkiness of the holding sealing material wrapped around the exhaust gas treating body.
As a mat used for the holding sealing material, JP-A 9-946 discloses a binder mat manufactured by impregnating a mat made of alumina fibers with an organic binder solution, and then drying the mat with hot air in a compression state.
The manufactured binder mat is cut into a predetermined shape to manufacture a holding sealing material.
JP-A 62-56348 discloses a mat made of alumina fibers.
The mat made of alumina fibers is manufactured by carrying out barb needling, in which barb needles having a plurality of barbs are inserted into and drawn from a precursor sheet formed by compressing unfired alumina fiber precursors in the thickness direction of the precursor sheet, to manufacture a needling precursor sheet having entangled portions, and firing the manufactured needling precursor sheet.
The manufactured mat is cut into a predetermined shape to manufacture a holding sealing material.
In the conventional binder mat described in JP-A 9-946, since inorganic fibers forming the binder mat are bonded to one another by an organic binder, the bulkiness of the binder mat is reduced.
Accordingly, it is believed that the bulkiness of the holding sealing material manufactured by cutting the conventional binder mat into a predetermined shape also reduces, and an exhaust gas treating body wrapped with the holding sealing material is more likely to be stuffed into a casing.
Further, it is believed that, during use of an apparatus for purifying exhaust gas, the organic binder is thermally decomposed by high-temperature exhaust gases to reconstruct the shape of the holding sealing material, and the exhaust gas treating body can be held well.
However, in the case where the conventional binder mat described in JP-A 9-946 is manufactured, due to good water-absorbing property and low air permeability of the non-woven mat, much time is required to volatilize a dispersion medium or solvent of an organic binder solution with dry air in a drying process, causing problems of the reduced manufacturing efficiency and the increased manufacturing cost of the binder mat.
In contrast, in the conventional mat described in JP-A 62-56348, since inorganic fibers are complicatedly entangled at a portion from and into which barb needle is drawn and inserted (entangled portion) along the thickness direction of the mat, the bulkiness of the mat is reduced around the entangled portion.
Accordingly, it is believed that the bulkiness of the holding sealing material manufactured by cutting the conventional mat into a predetermined shape is also reduced, and the exhaust gas treating body wrapped with the holding sealing material is more likely to be stuffed into the casing.
However, an increase in the bulkiness of the conventional mat described in JP-A 62-56348 is not sufficiently suppressed.
Therefore, the inventors of the present invention have applied the technology described in JP-A 9-946, impregnated the mat described in JP-A 62-56348 with an organic binder solution, and dried the mat with dry air to manufacture a binder mat. In this case, as is the case of manufacturing the conventional binder mat described in JP-A 9-946, the inventors have found that, due to good water-absorbing property and low air permeability of the non-woven mat, much time is required to dry the mat, causing problems of the reduced manufacturing efficiency and the increased manufacturing cost of the mat.
The contents of JP-A 9-946 and JP-A 62-56348 are incorporated herein by reference in their entirety.